Cognitive radio is one of the most popular wireless techniques. The emergence of the cognitive radio has changed the spectrum using way of exclusively using spectrum resources by a licensed user. Each cognitive user can perform interactive perception with the wireless communication environment and automatically changes its transmit-receive parameters, so that the authorized spectrum can be dynamically reused on the premise of ensuring the normal communication of the licensed user (primary user) and the utilization efficiency of the spectrum can be significantly improved. In addition, a multi-antenna way is recognized as one of the required technical schemes for further high-speed wireless networks. A multi-antenna communication system increases space dimension on the basis of original frequency domain, time domain and code domain, with the advanced space-time signal processing technologies, its capacity can be upgraded by times without increasing bandwidth and transmission power, in addition, the anti-interference and anti-fading performances of the communication system can be simultaneously enhanced, so that the scarce spectrum can be effectively eased and high-speed business support can be further provided. Both as the effective means for improving the spectrum efficiency, the combination of the multi-antenna technique and the cognitive radio technique can further realize very broad application prospects.
At present, there are two well-known spectrum access models for cognitive radio, namely the spectrum hole-based opportunistic spectrum access and the interference temperature-based spectrum sharing.
The spectrum hole-based opportunistic spectrum access is as follows: spectrum resources which are not used by the primary user in specific positions at specific times are called as spectrum holes, and the opportunistic spectrum access manner utilizes the spectrum holes to communicate, which is the direct realization of cognitive radio. This kind of access way does not need to control the transmission power, but a high-precision spectrum detection technique is required in the cognitive network; and when the traffic in primary network is busy, it is very difficulty to obtain the communication opportunity in the opportunistic spectrum access model.
The interference temperature-based spectrum sharing is as follows: interference temperature is defined at the front end of radio frequency of a wireless receiver, which is used for measuring the interference received by a receiver in a certain geographical position within a certain frequency band, and the maximum interference temperature which can be tolerated by normal communication of the receiver is called as an interference temperature boundary. As long as the interference from the cognitive network to the primary receiver can be controlled within the interference temperature boundary, the licensed frequency band can be reused by the cognitive user without affecting the normal communication of the primary user. By utilizing this kind of access way, the cognitive network and the primary user can simultaneously use the same licensed frequency band in the same position, but the transmission power of the cognitive network must be controlled to meet the interference temperature boundary of the primary user, so that the spectrum sharing way can not realize a large-range network coverage and the communication performance is very poor when the distance to the primary network gets shorter.